1. Field of the Invention
The present invention relates to a light emitting device (LED) and, in particular, to an electrode wiring section of a light emitting device.
2. Description of the Related Art
A conventional LED array head for an electrophotographic printer is disclosed, for example, in Japanese Patent Laid-Open No.60-48384, according to which the LED array head comprises LED arrays prepared on compound-semiconductor-monocrystal substrates each having a length of approximately 1 to 2 cm, and these LED arrays are arranged on a support substrate and adhered thereto.
FIG. 26 shows such a conventional LED array head comprising multiple LED arrays 403 which are arranged in a row on a support substrate 402 and adhered thereto. It is necessary to ensure a large space around the photosensitive drum 401 for the installation of the LED array head.
As a means for eliminating the need for such a large space, a structure has been proposed in which the monocrystal substrates are arranged such that the emission of light is effected in a direction parallel to the support substrate, with the support substrate being held perpendicular to the peripheral surface of the photosensitive drum (Japanese Patent Laid-Open No. 2-125765). With this structure, however, the mounting operation takes a long time since a large number of small compound-semiconductor-monocrystal substrates have to be arranged on the support substrate and adhered thereto while setting their optical axes in alignment with each other. Furthermore, the interval between the light emitting elements and the light emission intensity in the joint sections are liable to be rather uneven.
As a solution of this problem, the present inventors proposed a semiconductor device prepared by using a selective nucleation method.
According to the selective nucleation method, crystal growth is effected on a substrate having a free surface on which are arranged side by side the surface of an amorphous or polycrystalline non-nucleation layer having a small nucleation density, and parts of the surface of an amorphous or polycrystalline nucleation layer having a nucleation density larger than that of the non-nucleation layer, each of the parts of the latter surface having an area small enough for crystal growth to be effected starting from a single nucleus. Crystals are grown on this substrate, each starting from a single nucleus. With the selective nucleation method, however, crystal-growth conditions which will increase the monocrystallization factor lead to a deterioration in the occupation factor, whereas crystal-growth conditions which will increase the occupation factor lead to a deterioration in the monocrystallization factor. As a means for avoiding this dilemma, the present inventors also separately have proposed a selective semiconductor-device formation method using polycrystals.
FIG. 27 is a sectional view of a light emitting device prepared by the selective nucleation method.
A nucleation layer 203 is formed by evaporation on a heat resistant substrate 201, and a non-nucleation layer 202 is deposited on the nucleation layer 203 by evaporation. The non-nucleation layer 202 is then partly removed to expose parts of the nucleation layer 203. Then, a p-type semiconductor region 204 is formed by crystal growth around each of the exposed parts of the nucleation layer 203. Further, an n-type semiconductor region 205 is formed on each p-type semiconductor region 204 by crystal growth. An electrode 207 is connected to each p-type semiconductor region 204, which is situated on the inner side, and an electrode 206 is connected to each n-type semiconductor region 205, which is situated on the outer side.
A problem with the light emitting device formed by the conventional selective nucleation method, described above, is that there is a difference in level between the semiconductor crystal islands and the substrate surface on which the electrode wiring is provided for the electrodes outside the light emitting regions, with the result that the electrode wiring is liable to suffer disconnection.